Seafood Decision Guide

Seafood is often seen as one of the healthiest protein choices, but not all seafood is the same. The biggest difference comes down to how much a fish or shellfish accumulates over time, and the quality of the water and feed it comes from.

Small Wild-Caught / Lower Accumulation

Best overall seafood choice with the lowest buildup over time

Small Wild-Caught / Lower Accumulation

Best overall seafood choice with the lowest buildup over time

What it is Smaller wild-caught fish lower on the food chain

Source Shorter-lived species with lower bioaccumulation

Why it matters Lower likelihood of mercury and less buildup of compounds like PCBs and dioxins

These species generally accumulate fewer contaminants because they live shorter lives and feed lower on the food chain.

Higher-Quality Farmed or Lower-Risk Wild Options

Can still be a good choice, but sourcing matters much more

Higher-Quality Farmed or Lower-Risk Wild Options

Can still be a good choice, but sourcing matters much more

What it is Farmed or wild seafood with lower contamination risk when sourcing is stronger

Source Better-managed farms or lower-risk species

Why it matters Can still be lower in toxic burden, but water quality, feed, and sourcing matter more

This tier depends more on where it comes from. Good sourcing can lower risk, but quality varies much more than with smaller wild fish.

Larger Wild Fish / Higher Accumulation

Wild-caught does not always mean lower exposure

Larger Wild Fish / Higher Accumulation

Wild-caught does not always mean lower exposure

What it is Larger predatory fish that accumulate more over time

Source Higher on the food chain and longer-lived

Why it matters More likely to carry higher mercury levels and more buildup of compounds like PCBs and dioxins

As fish get larger and live longer, they tend to accumulate more contaminants in tissue over time.

Poorly Sourced Farmed or Highest-Accumulation Species

Highest likelihood of contaminants becoming part of what you eat

Poorly Sourced Farmed or Highest-Accumulation Species

Highest likelihood of contaminants becoming part of what you eat

What it is Seafood from lower-quality farmed systems or very high-accumulation species

Source More contaminated feed, poorer water conditions, or very high bioaccumulation

Why it matters Highest likelihood of mercury, PCBs, dioxins, and other contaminants becoming part of what you eat

This is the category where poor farming conditions or very high bioaccumulation make seafood the most exposure-prone.

How to think about seafood choices

Seafood is different from other foods because the main issue is not processing or coatings — it’s what builds up inside the animal over time.

In practical terms, focus on:

how large the fish is
how long it lives
where it sits in the food chain
whether it comes from clean water or controlled farming systems

Smaller, shorter-lived fish tend to carry less. Larger, longer-lived fish tend to carry more.

Where exposure comes from

Seafood exposure mainly comes from accumulation in the water and food chain.

As fish live and feed, they absorb compounds from their environment. Over time, these compounds can build up in their tissue.

The longer a fish lives and the higher it sits in the food chain the more it tends to accumulate.

This is why larger fish often carry higher levels of:

mercury (a heavy metal)
PCBs (polychlorinated biphenyls)
dioxins

These compounds are persistent, meaning they do not break down easily and can remain in the body over time.

In farmed seafood, there is an additional layer. Exposure can come from:

the quality of the water
the feed used in farming systems

Lower-quality farming environments can increase the likelihood of contaminants being present in the final product.
Over time, repeated intake of these compounds is associated with effects on the nervous system, hormone balance, and long-term metabolic health.

Quick seafood cheat sheet

If you want a simple way to apply this in real life, use this as a guide:

Better choices (lower buildup):

Sardines
Anchovies
Wild salmon (especially smaller varieties)
Mackerel (not king mackerel)
Herring

Middle ground (depends on sourcing):

Farmed salmon (quality varies by farm)
Shrimp (varies widely by source and country)
Cod, tilapia, trout

More caution (higher buildup):

Tuna (especially albacore and larger species)
Swordfish
King mackerel
Shark

This isn’t about avoiding seafood it’s about choosing types that carry less over time.

What to look for when buying seafood

You don’t need to overthink it — a few simple choices make a clear difference.

Choose smaller fish more often
Lower on the food chain and tend to carry less mercury, PCBs, and other contaminants

Be more selective with larger fish
Species like tuna, swordfish, and king mackerel tend to carry higher levels of mercury and other accumulated compounds

Pay attention to sourcing for farmed seafood
Water quality and feed can directly affect whether contaminants like PCBs and dioxins end up in the fish

Mix your choices
Rotating different types of seafood helps avoid repeated exposure from the same source

These simple shifts help reduce overall exposure while still getting the benefits of seafood.

Common labels explained

Wild-caught
Fish caught in natural environments. This does not always mean lower contamination — species and size still matter.

Farm-raised
Fish raised in controlled systems. Quality depends heavily on water conditions and feed.

Sustainably sourced
Focused on environmental impact and fishing practices. This does not always reflect contamination levels.

Bottom Line

With seafood, the main factor is how much the animal builds up over time. Smaller, shorter-lived fish tend to carry lower levels of compounds like mercury, PCBs, and dioxins. Larger fish and poorly sourced farmed seafood are more likely to carry higher levels of these contaminants.

The goal is to choose seafood that is lower on the food chain, comes from better sources, and carries a lower overall toxic burden.